This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-227482, filed Jul. 27, 2000; the entire content of which is incorporated herein by reference.
The present invention relates to an optical scanner of a type having a movable plate supported at a support body by means of torsion bars, and scanning light by turning the movable plate with the torsion bars being a turning axis.
The optical scanner of such type as described above is widely known in Jpn. Pat. Appln. KOKAI Publication No. 10-123449.
In an optical scanner 1 disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-123449, as shown in FIG. 12, a movable plate 2, torsion bars 3, and a support body 4 are integrally configured by utilizing a semiconductor process.
The movable plate 2 has a front portion provided with a coil 5 and a back portion having a reflection face. The front portion and back portion are configured in parallel to each other. The movable plate 2 is positioned at a neutral position in a stop state (in a non-driven state). The neutral position denotes a state in which the movable plate 2 is supported so that the front portion of the movable plate 2 and the front portion of the support body 4 (a face at the same side as the front portion of the movable plate 2) are substantially disposed on the same plane.
At this neutral position, the front portion of the pair of torsion bars 3 (a face at the same side as the front portion of the movable plate 2) as well is disposed at the substantially same plane as the front portions of the movable plate 2 and support body 4. In addition, at this neutral position, the mutually longitudinal center axis lines of the pair of torsion bars 3 are kept in a state in which these axis lines coincide with each other.
The torsion bars 3 are configured in the shape of a pair of plates, each of which is connected to the movable plate 2 at one end, and is connected to the support body 4 at the other end. A pair of torsion bars 3 has a longitudinal center axis lines, and is disposed in a straight line manner so that the mutually longitudinal center axis lines coincide with each other. The longitudinal center axis lines do not pass through the gravity of the movable plate at the neutral position.
The support body 4 supports the movable plate 2 so that the plate can be swung by means of the torsion bars 3. In addition, a pair of permanent magnets 6 is fixed to a face at the same side as the front portion of the movable plate 2.
The coil 5 is provided along the outer periphery at the front portion of the movable plate 2. Both ends of the coil 5 are pulled out onto the support body 4 over a pair of the torsion bars 3. One end and the other end of the coil 5 pulled out onto the support body 4 configure a power supply pad 5a. The power supply pad 5a is connected to a power source (not shown).
When a current is applied from the power supply pad 5a to the coil 5, the optical scanner 1 causes the movable plate 2 to swing (turn) with the torsion bars being a turning axis due to the Lorentz force (electromagnetic force) generated by a magnetic field formed by the permanent magnets 6 and the current. That is, the movable plate 2 is such that the longitudinal center axis lines of a pair of torsion bars 3 and the turning center line of the plate itself coincide with each other. The optical scanner 1 causes light to be externally incident to the reflection face of the back portion of the movable plate 2, and the thus incident light is reflected, thereby scanning light.
The above described optical scanner 1 makes the following operation when the scanner is subjected to strong shock due to a drop or is subjected to vibration.
Hereinafter, a force to which torsion bars 3 are subjected when the optical scanner 1 drops and is subjected to shock will be described with reference to FIG. 13.
First, referring now to FIG. 13A, a description is given with respect to a case in which the optical scanner 1 having the movable plate 2 set at the neutral position drops on a horizontal floor face while the back portion of the movable plate 2 is horizontal. In the specification, the drop is defined as a first state drop.
The first state drop denotes a drop in a vertical direction (a drop downward on a paper face) while the back portion of the movable plate 2 is horizontal. Thus, this drop can be referred to as a drop in a direction orthogonal to the back portion.
When the first state drop is carried out, at a moment when the optical scanner 1 collides with the floor face, an inertial force caused by multiplying acceleration due to such drop for the mass of the movable plate 2 is applied to the movable plate 2. At this time, the movable plate 2, as shown in FIG. 13A, is displaced in a direction (downward) orthogonal to the back portion of the movable plate 2. In the case where the inertial force is excessive, a stress equal to or greater than a permissible stress generates with a pair of torsion bars 3. In this case, the torsion bars 3 extend downwardly or are bent, and a permanent deformation generates. Due to this permanent deformation, there is a possibility that a damage or characteristic change generates with the torsion bars 3. In the case where such a damage or characteristic change generates with the torsion bars 3, the optical scanner 1 cannot cause the movable plate 2 to perform desired swinging, and desired optical scanning cannot be performed. That is, the optical scanner 1 is damaged or is changed in characteristics.
In addition, at the first state drop, although the back portion is positioned downwardly, the front portion may be positioned downwardly. In the case where the optical scanner drops when the front portion is positioned downwardly, the scanner is displaced in a direction orthogonal to the front portion. In this case as well, as in the case where the above described back portion is positioned downwardly, the torsion bars 3 extend downwardly or is bent, and there is a possibility that a permanent deformation generates.
In the specification, a displacement of the movable plate in a direction orthogonal to the front portion and/or back portion is defined as an orthogonal displacement.
Now, a description will be given with respect to a drop of the optical scanner at a disposition at which the surfaces (front portion and back portion) of the movable plate 2 are vertical, in the optical scanner 1 having a movable plate 2 set at a neutral position. In the specification, the above described drop is defined as a second state drop.
The second state drops include a second state horizontal drop in a state in which torsion bars 3 are horizontal (more precisely, the longitudinal center axis lines of the torsion bars are horizontal) and a second state vertical drop in a state in which the torsion bars 3 are vertical.
Now, the second state horizontal drop will be described hereinafter.
With respect to the second state horizontal drop, in FIG. 13B, the drop direction is schematically indicated by the arrow F. When the second state horizontal drop is carried out, at a moment when the optical scanner 1 collides with a floor face H, an inertial force is applied to the movable plate 2 as in the first state drop. Here, the gravity of the movable plate 2 does not coincide with the longitudinal center axis lines of the torsion bars 3. Thus, the inertial force acts as a moment relevant to the rotation axis. Therefore, a deformation due to expansion and torsion generates with the torsion bars 3. As indicated by the arrow R shown in FIG. 13Bxe2x80x2, the movable plate 2 turns around the turning axis with the torsion bars 3 being the turning axis. In the specification, this turning movement is defined as a turning displacement. In the case where the inertial force is excessive, a permanent deformation due to expansion and torsion generates with the torsion bars 3 due to such turning displacement. Thus, there is a possibility that a damage or characteristic change generates with the optical scanner 1.
In addition, in the second state horizontal drop, the movable plate 2 may be displaced differently from the turning displacement described previously. In particular, in a configuration in which the longitudinal center axis lines of the torsion bars 3 pass through the gravity of the movable plate 2 (applicable to any other configuration), the movable plate 2 may be displaced in a direction orthogonal to the longitudinal center axis lines along the front portion and/or back portion, as shown in FIG. 13D. In the specification, this displacement is defined as an axially orthogonal displacement. In the case where the inertial force is excessive, a permanent deformation due to expansion generates with the torsion bars 3 due to this axially orthogonal displacement. Thus, there is a possibility that a damage or characteristic change generates with the optical scanner 1.
Now, the second state vertical drop will be described here.
The second state vertical drop denotes a drop of the optical scanner 1 onto a floor face H while the longitudinal center axis lines of the pair of torsion bars 3 are orthogonal (vertical) to horizontal face. With respect to the second state vertical drop, in FIG. 13C, the drop direction is schematically indicated by the arrow F.
When the second state vertical drop is carried out, at a moment when the optical scanner 1 collides with a floor face H, an inertial force is applied to the movable plate 2 as in the first direction drop. Therefore, a deformation due to expansion and torsion generates with the torsion bars 3. As shown in FIG. 13Cxe2x80x2, the movable plate 2 is displaced so as to be inclined relevant to the front portion of the support body 4 at a vertical cross section at which its own front portion passes through the turning center line. In the specification, this displacement is defined as an inclined displacement. In the case where the inertial force is excessive, a permanent deformation due to expansion and bending generates with the torsion bars 3 due to this displacement. Thus, there is a possibility that a damage or characteristic change generates with the optical scanner 1.
In addition, in the second state vertical drop, the movable plate 2 may be displaced differently from the inclined displacement described previously. In particular, in a configuration (applicable to any other configuration) in which the longitudinal center axis lines of the torsion bars 3 pass through the gravity of the movable plate 2, the movable plate 2 may be displaced in a direction along the longitudinal center axis lines along the front portion and/or back portion, as shown in FIG. 13E. In the specification, this displacement is defined as an axial displacement. In the case where an inertial force is excessive, a permanent deformation due to expansion or compression generates with the torsion bars 3 due to this axially orthogonal displacement. Thus, there is a possibility that a damage or characteristic change generates with the optical scanner 1.
In the specification, a displacement denotes a change in movement and posture from the neutral position of a movable plate. In addition, the displacement includes a movement such that a linear and curved route is traced and a combination with a change in posture.
As has been described above, if the movable plate 2 is displaced excessively over a predetermined movable region, a plastic deformation or crack generates with the torsion bars 3 in the optical scanner 1. There is a possibility that a damage or characteristic change caused by swinging of the movable plate 2 generates. The present invention has been made in view of the foregoing problem. It is an object of the present invention to provide an optical scanner capable of preventing a damage or characteristic change even if the scanner is subjected to extreme shock or vibration.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.